The invention relates to a balancing arrangement, and more particularly to an improved balancing arrangement for hollow drive shafts which allows for the compensation of greater imbalances.
Balancing arrangements of various types are known in the prior art. For example, U.S. Pat. No. 3,901,046 to Hofmann discloses a balancing arrangement utilizing a clip to be tightened on the rotating member whereby counterweights are affixed to the clip within an area substantially opposite the connection of the free ends of the clip by means of a screw-type (worm-drive) connection. This type of arrangement is relatively complicated in installation because of the time-consuming determination of the imbalance and is also relatively inefficient because the counterweight must always offset also the screw-type connection of the open ends of the clip.
My prior U.S. application Ser. No. 07/446,812 avoids the shortcomings and drawbacks of Hofmann by placing the counterweight within the area of the mechanical connection of the open clamping band. With the earless construction as disclosed in FIGS. 1-5 of this application, sections having concavely shaped lateral band portions with an hourglass-like window defined therebetween are used to impart elastic stretchability in the longitudinal direction to the clamping band to compensate for thermal fluctuations of the drive shaft. The counterweight is thereby affixed to the clamping band by hook-like projections. In the embodiment of FIGS. 6-12, of the application Ser. No. 07/446,812, the tightening member is constituted by a plastically deformable ear whereby in FIGS. 10-12 the ear is made in one piece with the counterweight.
The U.S. Pat. No. 5,230,246 differs from the aforementioned copending application by a special construction of the plastically deformable ear which is provided with tab-like members intended to perform the dual function of avoiding problems in case of positional changes of the balancing arrangement and of increasing the strength of the ear-like member.
Hollow drive shafts are made to specified dimensions with a given accuracy. However, the greater the permissive tolerance in the external dimensions of the shaft, i.e., the greater the possible imbalance in the drive shafts, the greater must be the weight range of the counterweights to compensate for the imbalance. In other words, if drive shafts can be manufactured with lesser accuracy in the external dimensions which is desirable from a manufacturing cost point of view, then it becomes important to provide a balancing arrangement which is capable of securely handling counterweights of greater weight.
Recent developments have indicated a need to double the size of the maximum weight of the counterweight to be usable in the balancing arrangement. However, this goal has appeared unattainable with balancing arrangements as disclosed in the copending application Ser. No. 07/446,812 and the U.S. Pat. No. 5,230,246.
It is therefore a principal object of the present invention to provide a balancing arrangement and a preassembled clamp structure with an integral balancing counterweight which efficiently obviates the shortcomings and drawbacks encountered with the prior art constructions and assures reliable secure holding of counterweights with double the weight contemplated heretofore.
The underlying problems are solved according to this invention by a specific arrangement of the combination of clamp structure and counterweight. More specifically, the mechanical connection of the clamp structure must be able to withstand greater tightening forces for the increased weight of the necessary maximum counterweights and, with the use of a so-called xe2x80x9cOetikerxe2x80x9d ear, the holding ability of the ear must also be substantially increased.
It has also been discovered that for most purposes, so-called xe2x80x9cOetikerxe2x80x9d ears are able to provide sufficient compensation for thermal temperature changes of the drive shaft so that it is sufficient to provide elasticity on the part of the clamping band by the use of a clamping band of generally concave shape in transverse cross section. Elasticity may also be imparted to the counterweight by the use of a radius of curvature of its internal surface slightly smaller than the radius of curvature of the drive shaft.
A surprisingly greater holding ability of a clamp with a so-called xe2x80x9cOetikerxe2x80x9d ear is attained by utilizing two side-by-side longitudinally extending reinforcing grooves having each a rounded-off bottom and delimited by substantially parallel side surfaces interconnected by semi-circular end surfaces, especially also with the use of a wider clamping band than normally used heretofore. A satisfactory holding ability could be attained with these modifications.
In case of the use of a so-called earless clamp in such a balancing arrangement, a strong mechanical connection of the clamp can be achieved with the use of a new support hook engaging from below into a tunnel-shaped aperture to securely hold the earless clamp structure in its installed and fully tightened position. The improved support hook offers greater resistance against buckling or collapse of the hook under the load of the outer clamping band portion during tightening and at the same time facilitate the sliding movement of the outer clamping band portion over a flat top portion in the novel support hook during tightening.
Additionally, it has also proven advantageous to connect the counterweight permanently to the clamping band by spot welding within the area of the inner band end portion between the mechanical connection and the free end in the inner band portion which permits an inexpensive and efficient preassembly of counterweight and clamp structure. In the alternative, a simple mechanical connection within the same area with a centering arrangement of the counterweight may be used in a modified embodiment of this invention.
In the case of a so-called earless clamp structure, a pressed-out reinforcement in the area of the free end of the outer band portion has also proved highly successful to avoid lifting up of the band during tightening of the clamp structure and to improve the stability of the tunnel-shaped member located near the free end of the outer band portion and involved in the tightening of the clamp structure.
In order to improve the effectiveness of the counterweight, the area of the clamping band opposite the mechanical connection and of the counterweight may be subjected to a weight reduction by the removal of clamping band material with the use of openings of various sizes, shapes and dimensions as well as of a varying number of such openings, as will be described more fully hereinafter.